ZETA SERIES – HARDBOUND SKETCHBOOKS Stillman & Birn Zeta Series Hardbound Sketchbooks, 270 gsm (Extra Heavyweight), white paper, smooth surface. Suitable for dry and wet media, watercolour and ink. Example of recommended usage: detailed pen & ink line work combined with liberal applications of watercolour. A favourite of botanical artists and illustrators. Acid-free, chloride-free, lignin-free.